As a rustproofing agent for car underbodies, parts around tires, parts with pockets, and plate-bonded parts, rustproofing agents in which wax and several kinds of additives are dissolved or dispersed in organic solvents such as mineral spirits, that is, wax-type rustproofing agents, have been used. Compositions which can be applied thick are also used as long-term rustproofing agents for metallic materials outdoors, since high rustproofing ability is exhibited. In addition, a rustproofing oil which does not contain much wax component or petrolatum component is unsuitable for long-term rustproofing, since it cannot be applied thickly.
As a conventional wax-type rustproofing agent, for example, compositions with improved coating ability are disclosed in Japanese Unexamined Patent Application Publications Nos. S60-40159 and H1-92267, and a composition which improves production technology is disclosed in Japanese Unexamined Patent Application Publication No. S61-55198. However, when these wax-type rustproofing agents are used for rustproofing plate-bonded parts, it is necessary to adjust the viscosity to be low in order to ensure sufficient permeability into narrow gaps, and it is necessary to have a time in which viscosity is increased by evaporation of solvent to some extent in order to prevent running after application. Additionally, in order to improve permeability and spray workability, in these compositions, organic solvents such as mineral spirits are used as solvents for dilution and dispersion so as to adjust viscosity. There are cases in which the content of the organic solvents exceeds 70 weight %. Furthermore, in the case in which the compositions are applied thickly to car underbodies or parts around tires, there is a problem in that the applied agents are not dried easily and are sticky forever. That is, the compositions are applied and the wax coating which is a semi-hard coating is formed by evaporating the organic solvent into the air. Because such evaporated organic solvents are recently considered to be one of the causes of global warming, research to reduce organic solvents which are used in coatings is often performed and movements to regulate the amount of volatile organic solvent by law are increasing. Some rustproofing compositions which satisfy the above demands are proposed in Japanese Unexamined Patent Application Publication No. 2003-268574 and Japanese Patent Application No. 2004-192873.
However, in the case in which organic solvents evaporated from the wax-type rustproofing agents are simply reduced, the viscosity of the agents is increased and sufficient permeation into gaps cannot be obtained. Therefore, in conventional technology, non-volatile component content was limited to 80 weight % in order to maintain sufficient permeation and prevention of running is inferior. Furthermore, as a method to reduce organic solvents evaporated from the wax-type rustproofing agent, a method in which the organic solvent used in the compositions is substituted by high-viscosity oil having low volatility was examined. However, in this method, the coated film did not dry so as to run forever, the coated film flowed off under high temperatures or vibrations, the coated film was easily removed by a physical force such as contact with water or the like, and sufficient rustproofing ability could not be obtained.
In addition, as a method to reduce organic solvent, a method in which water-based rustproofing component is used was suggested. However, when the water-based rustproofing agents were applied to pockets in parts of car bodies or plate-bonded parts, water which was contained in the permeated compositions could not be evaporated and rust was generated. Furthermore, a rust preventing method in which a wax composition in a solid state at normal temperatures is heated to melt and is coated by dipping these parts into the melted wax, or a rust preventing method in which melted wax is used, was developed. However, such methods require large-scale equipment, and large amounts of heat are required to melt the solid wax, and these methods therefore have problems in cost efficiency.